Marriages between Catholics and spouses of other religions, once sharply discouraged, have increased to the point where approximately two out of every five Catholic marriages are interreligious.

Nearly three quarters of Americans approve of interreligion marriages, with Catholics more likely than Protestants to approve.

These are among the conclusions drawn from a review of 70 research studies on interreligion marriages during the last 40 years. The survey was conducted by DEAN R. Hoge and KATHLEEN M. Ferry of the Boys Town Center for the Study of Youth Development, located at Catholic University.

The researchers discovered that marriages between a Protestant and a Catholic are more likely to end in divorce than either Protestant or Catholic same-religion marriages. But they note that "it is unclear whether mixing religions is a cause of instability, or just another characteristic of people who are less likely to have stable marriages of any kind."

Interreligion marriages in which one spouse converts to the other's faith tend to have a better chance, the study indicated.

Some of the other findings of the study, which concentrated on intermarriages involving one Catholic partner, were:

People are most likely to intermarry if their ties are to religion are weak or unconventional, if they have inadequate family ties, or if they marry very young.

Persons who have been married before are more likely to marry outside their church.

More Catholics marry outside their church in regions where there are relatively few Catholics in the total population. But the study also found that Catholics generally marry outside their faith at a higher rate than either Protestants or Jews.

In half of all interreligion marriages involving Catholics, one spouse converts to the others religion. In the past, strict church laws governing interreligion marriage meant that most of the conversions were to Catholicism. But with the relaxation of such regulations in recent years, Hoge and Ferry said, "It appears that the pattern has now evened out, with fewer Protestants and more Catholics converting."

In marriages where one-spouse does convert, nearly all conversions take place at the time of marriage or before the couple's first child is 10 years old.

The most common causes of dissension in interreligion marriages are "lack of companionship and disagreement over children's religious upbringing," the researchers said.

With both Protestants and Catholics, the researchers said, the mother has a stronger influence on the children's religious identification than the father.